7.6.3 Estimation of risk from low-level radiation

Because of the very low level of exposure resulting from consumption of drinking water containing radionuclides, and the radionuclides involved, it is not possible to distinguish a radiation-induced cancer incidence from the baseline level of cancers in the general population. The theoretical water consumption health risk is estimated by extrapolation from the proven effects at doses that are orders of magnitude higher than those typically received through water consumption.

Radiation protection is based on a conservative model that assumes that any exposure to radiation involves some level of risk. It is assumed that there is a linear relationship between exposure and risk, with no threshold value below which there is no risk. For prolonged exposures over extended periods of time, evidence of an increased cancer risk in humans is well quantified at doses above 100 mSv (Brenner et al. 2003, UNSCEAR 2018). For radiation exposures below 100 mSv the scientific evidence for increased health risk is more limited. The available epidemiological studies do not show any health effects of radionuclides at levels naturally encountered in drinking water (Guseva Canu et al. 2011). While this conservative linear no threshold model can be used to infer health risks associated with low radiation doses and dose rates, projections of absolute number of cancer cases in a population may not be valid and could be increasingly misleading as doses decrease (RHSAC 2017, ICRP 2007).

Any theoretical increase in genetic disorders (including birth defects) is expected to be much less than any theoretical increase in the cancer rate and therefore an acceptable dose level for cancer risk will also be protective for genetic risk.